The present invention relates to a solid state image sensor and, more particularly, to a contact-type image sensor having a linear cell array of amorphous semiconductor photoelectric converting elements, which are switch-driven using a matrix drive technique.
Amorphous semiconductor image sensors are preferably used for various types of optical image reading equipment such as a facsimile system, an optical code reader, a copying machine, etc., since the use of such image sensors makes it possible to miniaturize the equipment. In particular, considerable effort has been given to the development of contact-type solid state linear image sensors having substantially the same length as the width of paper documents to be read. Such image sensors offer an advantage over other kinds of imaging devices in that they can eliminate image reduction that uses a lens system before the document image reaches thereto, so that the optical image reading equipment can be made compact in size.
The contact-type amorphous semiconductor image sensor is usually connected to a matrix circuit and switch-driven by a matrix drive technique. In this case, linearly aligned photoelectric converting elements serving as pixels (picture elements) are divided into pixel groups or cell units, which are connected at their first comb-shaped planar electrodes serving as individual cell electrodes to an image signal detector, through a matrix wiring circuit consisting of crossed row and column signal lines. In each pixel group a second comb-shaped planar electrode is provided to serve as a common electrode therefor. The second comb-shaped planar electrodes of pixels are connected to a drive voltage generator. The photoelectric converting elements are successively selected with each pixel group as a unit, so that time sequential video signals may be obtained by the image signal detector.
According to the conventional image sensor, an amorphous silicon layer is provided on a substrate to serve as a photoelectric converting layer for photoelectric converting elements. Image light incident on the photoelectric converting elements is sensed utilizing a photoconductive effect of the amorphous silicon layer. The amorphous silicon layer is formed to cover the predetermined surface region on the substrate using a thin film fabrication technique such as a chemical vapor deposition or CVD method and an etching technique, which are similar to a method of manufacturing a semiconductor IC. More specifically, an amorphous silicon layer is deposited on the entire top surface of a single substrate. Subsequently, most of the amorphous silicon layer thus deposited is removed, except part of a desired region, by an etching technique. As a result, the amorphous silicon layer may be formed only in the surface region of the substrate occupied by the photoelectric converting elements. Electrical circuits such as a matrix wiring/drive circuit and a signal readout circuit are formed on the substrate surface from which the amorphous silicon layer is removed.
However, a conventional image sensor in which the photoelectric converting elements are formed together with peripheral electrical circuits on the single substrate has a problem of low productivity. This problem is caused since the amorphous silicon layer must be deposited once on the entire surface of the substrate. Since an area of the amorphous silicon layer which can be deposited at one time is limited in a CVD system, the number of substrates of a single-substrate-type image sensor which can be CVD-grown at the same time in the CVD system is reduced, resulting in poor packaging efficiency of the substrates in the CVD system. As a result, productivity of the image sensor is degraded to undesirably increase the manufacturing cost.
In order to cope with the problem, it is proposed that an image sensor substrate is divided into a first substrate for forming a sensor unit (photoelectric converting element unit) and a second substrate for forming a peripheral electrical circuit arrangement including a matrix wiring and a signal readout circuit and the like. In this case, since area of the separated first substrate for forming the sensor unit housed in the CVD system for growing the amorphous silicon layer is reduced (miniaturized) by approximately 50%, packaging efficiency of the substrates in the CVD system and productivity relating to formation of the amorphous silicon layer are improved. The first substrate is thereafter subjected to an etching process, in which the amorphous silicon layer is fabricated to obtain a desired planar shape, thereby obtaining the photoelectric converting elements serving as the sensor unit.
The method of dividing the substrate into two separated substrates improves productivity of the image sensor, but it poses another problem in that an arrangement for electrically connecting the separated substrates is complex. Normally, in order to electrically connect the substrates, thin wide flexible connectors are used. However, these flexible connectors occupy a large space in the image sensor, thereby degrading packaging efficiency. As a result, compactness, an essential merit of the image sensor, is degraded, and its operational reliability is also degraded.